
Writing a classic study of the nature of war usually goes like this. A devastating conflict happens. In the aftermath, military thinkers interpret how war, and the way it's fought, has changed. The emphasis is on a fundamental break with the past.
Clausewitz, for instance, considered that the bloodletting of the Revolutionary and Napoleonic wars was one such fracture. He believed that these conflicts approached the theoretical state of total war - "untrammelled by any
conventional restraints, broken loose in all its elemental fury". Writing after the First World War, Liddell Hart and Fuller articulated visions of a new form of conventional war based on emerging tactics, technologies and ideologies. Since the Cold War, strategists have written about emerging (or re-emerging) trends in conflict, like counterinsurgency, "war among the people", and cyber-conflict.
Niccolò Machiavelli's The Art of War (1521) is different. It starts with the view that contemporary military practice in Renaissance Europe is degenerate, and that if generals and statesmen wish to conduct wars effectively, they should look to the distant past for inspiration, to a golden age of military endeavour - ancient Rome and Greece...
"Cosimo: I should be very happy to learn if you have ever considered how it comes to pass that we are so degenerate, and that not only these exercises but all manner of military discipline, have now fallen into such neglect and disuse among us."
When you read The Art of War you realize that Machiavelli aimed to popularize classical military thought, principally the work of Vegetius (the late Roman author of De Re Militari), Polybius, Frontinus and Livy. He wanted to educate Renaissance commanders, who, he believed, were "strangers to all sorts of discipline and military knowledge", so that they could apply ancient wisdom to modern war.
Even with this in mind, it's surprising that Machiavelli makes relatively little reference to contemporary military practices and events. Most of the examples he uses to illustrate points derive from ancient times, like this comment on recruitment...
"Some, like Pyrrhus, would have their soldiers tall; others like Julius Caesar, prefer men who are active and vigorous."
This is strange given that the protagonist of The Art of War, the Italian mercenary captain Fabrizio Colonna, was an experienced soldier who'd fought for different masters in Italy. In a discussion on war you'd expect Colonna to draw on his own experiences, and those of his contemporaries, not ancient examples that he could know about only through books.
The same goes for Machiavelli himself. Although not a soldier, Machiavelli was well-versed in military affairs. He was active in Florence's siege of Pisa in 1509, and raised a Florentine militia which was modelled on ancient Greek and Roman armies. Machiavelli believed that citizen militias, when properly armed, trained and led, were superior to the mercenary forces of his day. He also considered that a militia acts as a bulwark against tyranny in a republic or principality, and is important for instilling civic pride and duty in citizens and subjects.
It's this kind of observation, not the commentary on ancient military practices, which makes The Art of War worth reading. If you want to study ancient military history, don't read Machiavelli; read Livy, Caesar, Xenophon, along with modern historical interpretations (Adrian Goldsworthy's In the Name of Rome is an excellent study of Roman generals). The same goes for medieval and Renaissance warfare.
For me, The Art of War is valuable for its discussion of the relationship between war and politics, the importance of a sound defence policy, and the appropriate role of military advisers in government. It's a good companion to Machiavelli's political works, The Prince and The Discourses.
Machiavelli reminds us that effective defensive capabilities are essential for any state that wants to safeguard its sovereignty, preserve the liberty of its citizens, and protect its interests and resources. Nor should defence policy be the preserve of elites and warrior castes within a state. The dangers of armed men seizing power, or advising rulers "to make war because they cannot support themselves without war", are as relevant today as they were 600 years ago.